As a technique of dilating a stenosed portion formed in a blood vessel of a living body, there are widely known so-called percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA) performed by using a balloon catheter.
In the technique using a balloon catheter, a guide wire is first inserted to a stenosed portion. Subsequently, the balloon catheter is caused to creep along the guide wire so that the balloon catheter is thrust into the stenosed portion in its entirety. Then, a balloon is inserted to the stenosed portion. Thereafter, the balloon is filled with a dilation fluid, and the balloon is dilated by increasing a pressure inside the balloon. Then, the stenosed portion is widened, thereby restoring blood flow.
Such a balloon catheter has an inner tube shaft as a medical tube in which the guide wire is inserted through an inner circumference, and an outer circumference of the shaft on a distal side is heat-welded with the balloon. It is preferable to form an inner layer of the inner tube shaft with high density polyethylene (HDPE) having low friction resistance against the guide wire in a view point of insertion properties of the guide wire. It is preferable to form an outer layer of the inner tube shaft with polyamide in a view point of flexibility of the balloon catheter and heat-welding properties with respect to the balloon.
However, in general, a material such as HDPE having low friction resistance against the guide wire and a material such as polyamide that exhibits excellent flexibility and heat-welding properties have poor bonding properties with respect to each other. Therefore when the inner tube shaft is configured to have a concentric double-layered structure, there may be an occurrence of separation between two layers due to relatively low stress (bending, butting, and pressurizing of the balloon) loaded thereon.
In this regard, for example, U.S. Pat. No. 6,165,166 discloses a flexible tube in which an intermediate joint layer is provided between the outer layer and the inner layer. According to the flexible tube, since the intermediate joint layer has bonding properties with respect to the outer layer and the inner layer, the outer layer and the inner layer are indirectly joined. Thus, the outer layer and the inner layer can be prevented from being separated from each other.